The heterotrimeric G protein transducin is central to the chain of reactions that lead to visual excitation and recovery. The interface between photoreceptor disk membranes and the cytoplasm provides the milieu in which these reactions occur. The structural and dynamic properties of the membrane protein complexes responsible for these reactions will be explored using biochemical assays, electron microscopy, spectroscopy, and photobleaching recovery. The characterization of these complexes will provide new insights into how vision normally functions, and into how defects in the molecules that form these complexes lead to retinal disease. They will also help us to understand how other G protein mediated complexes work, in the G protein-mediated pathways that comprise the most common mechanism of signal transduction in humans, and the most common targets of drugs.